Mitt Romney will address the GOP presidential race in a surprise speech Thursday

Mitt Romney's giving a surprise speech about the 2016
presidential race on Thursday.

The former governor of Massachusetts and 2012 GOP presidential
nominee will address the Hinckley Institute of Politics at the
University of Utah in Salt Lake City on Thursday, according to
his office.

Romney has yet to endorse a candidate, although it was rumored
last month that he'd endorse Florida Sen. Marco Rubio. Rubio's
camp later denied those rumors.

In recent days, Romney has engaged in a back and forth with GOP
frontrunner Donald Trump, whom he's denounced for failing to
distance himself from a Ku Klux Klan endorsement and for not
releasing his taxes.

"A disqualifying & disgusting response by @realDonaldTrump to
the KKK. His coddling of repugnant bigotry is not in the
character of America," Romney
tweeted on Monday after Trump said that he didn't know
enough about former KKK Grand Wizard David Duke or white
supremacists to denounce them.

Trump later said that it was because of a faulty earpiece.

On taxes, Romney has repeatedly said that Trump could be hiding a
"bombshell" in his returns.

Well, I think there's something there. Either he's not
anywhere near as wealthy as he says he is, or he hasn't been
paying the kind of taxes we would expect him to pay. Or perhaps
he hasn't been giving money to the vets or the disabled, like
he's been telling us he's been doing.

Trump has unleashed multiple tirades against Romney on
social media and in public.

Last week, he tweeted that Romney was
one of the "dumbest and worst" Republican candidates to ever
run for president.

"I criticized Mitt Romney for losing that election. He should
have won that election," Trump
said during last week's GOP debate in Houston, Texas.

"He ran a terrible campaign," he added. "He was a terrible
candidate. That's what I criticized Mitt Romney [for]. He ran one
terrible campaign! That's an election that should have been won."